// Copyright 2022 ByteDance Ltd. and/or its affiliates.
/*
 * Acknowledgement: This file originates from abseil-cpp.
 * https://github.com/abseil/abseil-cpp/blob/master/absl/strings/string_view.h
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
#include <matxscript/runtime/container/string_view.h>

#include <algorithm>
#include <climits>
#include <cstring>
#include <ostream>

namespace matxscript {
namespace runtime {

namespace {
void WritePadding(std::ostream& o, size_t pad) {
  char fill_buf[32];
  memset(fill_buf, o.fill(), sizeof(fill_buf));
  while (pad) {
    size_t n = std::min(pad, sizeof(fill_buf));
    o.write(fill_buf, n);
    pad -= n;
  }
}

class LookupTable {
 public:
  // For each character in wanted, sets the index corresponding
  // to the ASCII code of that character. This is used by
  // the find_.*_of methods below to tell whether or not a character is in
  // the lookup table in constant time.
  explicit LookupTable(string_view wanted) {
    for (char c : wanted) {
      table_[Index(c)] = true;
    }
  }
  bool operator[](char c) const {
    return table_[Index(c)];
  }

 private:
  static unsigned char Index(char c) {
    return static_cast<unsigned char>(c);
  }
  bool table_[UCHAR_MAX + 1] = {};
};

// This is significantly faster for case-sensitive matches with very
// few possible matches.  See unit test for benchmarks.
const char* memmatch(const char* phaystack, size_t haylen, const char* pneedle, size_t neelen) {
  if (0 == neelen) {
    return phaystack;  // even if haylen is 0
  }
  if (haylen < neelen)
    return nullptr;

  const char* match;
  const char* hayend = phaystack + haylen - neelen + 1;
  // A static cast is used here to work around the fact that memchr returns
  // a void* on Posix-compliant systems and const void* on Windows.
  while ((match = static_cast<const char*>(memchr(phaystack, pneedle[0], hayend - phaystack)))) {
    if (memcmp(match, pneedle, neelen) == 0)
      return match;
    else
      phaystack = match + 1;
  }
  return nullptr;
}

}  // namespace

std::ostream& operator<<(std::ostream& o, string_view piece) {
  std::ostream::sentry sentry(o);
  if (sentry) {
    size_t lpad = 0;
    size_t rpad = 0;
    if (static_cast<size_t>(o.width()) > piece.size()) {
      size_t pad = o.width() - piece.size();
      if ((o.flags() & o.adjustfield) == o.left) {
        rpad = pad;
      } else {
        lpad = pad;
      }
    }
    if (lpad)
      WritePadding(o, lpad);
    for (auto& c : piece) {
      if (c == 0) {
        o.write("\\x00", 4);
      } else {
        o.put(c);
      }
    }
    if (rpad)
      WritePadding(o, rpad);
    o.width(0);
  }
  return o;
}

string_view::size_type string_view::find(string_view s, size_type pos) const noexcept {
  if (empty() || pos > length_) {
    if (empty() && pos == 0 && s.empty())
      return 0;
    return npos;
  }
  const char* result = memmatch(ptr_ + pos, length_ - pos, s.ptr_, s.length_);
  return result ? result - ptr_ : npos;
}

string_view::size_type string_view::find(char c, size_type pos) const noexcept {
  if (empty() || pos >= length_) {
    return npos;
  }
  const char* result = static_cast<const char*>(memchr(ptr_ + pos, c, length_ - pos));
  return result != nullptr ? result - ptr_ : npos;
}

string_view::size_type string_view::rfind(string_view s, size_type pos) const noexcept {
  if (length_ < s.length_)
    return npos;
  if (s.empty())
    return std::min(length_, pos);
  const char* last = ptr_ + std::min(length_ - s.length_, pos) + s.length_;
  const char* result = std::find_end(ptr_, last, s.ptr_, s.ptr_ + s.length_);
  return result != last ? result - ptr_ : npos;
}

// Search range is [0..pos] inclusive.  If pos == npos, search everything.
string_view::size_type string_view::rfind(char c, size_type pos) const noexcept {
  // Note: memrchr() is not available on Windows.
  if (empty())
    return npos;
  for (size_type i = std::min(pos, length_ - 1);; --i) {
    if (ptr_[i] == c) {
      return i;
    }
    if (i == 0)
      break;
  }
  return npos;
}

string_view::size_type string_view::find_first_of(string_view s, size_type pos) const noexcept {
  if (empty() || s.empty()) {
    return npos;
  }
  // Avoid the cost of LookupTable() for a single-character search.
  if (s.length_ == 1)
    return find_first_of(s.ptr_[0], pos);
  LookupTable tbl(s);
  for (size_type i = pos; i < length_; ++i) {
    if (tbl[ptr_[i]]) {
      return i;
    }
  }
  return npos;
}

string_view::size_type string_view::find_first_not_of(string_view s, size_type pos) const noexcept {
  if (empty())
    return npos;
  // Avoid the cost of LookupTable() for a single-character search.
  if (s.length_ == 1)
    return find_first_not_of(s.ptr_[0], pos);
  LookupTable tbl(s);
  for (size_type i = pos; i < length_; ++i) {
    if (!tbl[ptr_[i]]) {
      return i;
    }
  }
  return npos;
}

string_view::size_type string_view::find_first_not_of(char c, size_type pos) const noexcept {
  if (empty())
    return npos;
  for (; pos < length_; ++pos) {
    if (ptr_[pos] != c) {
      return pos;
    }
  }
  return npos;
}

string_view::size_type string_view::find_last_of(string_view s, size_type pos) const noexcept {
  if (empty() || s.empty())
    return npos;
  // Avoid the cost of LookupTable() for a single-character search.
  if (s.length_ == 1)
    return find_last_of(s.ptr_[0], pos);
  LookupTable tbl(s);
  for (size_type i = std::min(pos, length_ - 1);; --i) {
    if (tbl[ptr_[i]]) {
      return i;
    }
    if (i == 0)
      break;
  }
  return npos;
}

string_view::size_type string_view::find_last_not_of(string_view s, size_type pos) const noexcept {
  if (empty())
    return npos;
  size_type i = std::min(pos, length_ - 1);
  if (s.empty())
    return i;
  // Avoid the cost of LookupTable() for a single-character search.
  if (s.length_ == 1)
    return find_last_not_of(s.ptr_[0], pos);
  LookupTable tbl(s);
  for (;; --i) {
    if (!tbl[ptr_[i]]) {
      return i;
    }
    if (i == 0)
      break;
  }
  return npos;
}

string_view::size_type string_view::find_last_not_of(char c, size_type pos) const noexcept {
  if (empty())
    return npos;
  size_type i = std::min(pos, length_ - 1);
  for (;; --i) {
    if (ptr_[i] != c) {
      return i;
    }
    if (i == 0)
      break;
  }
  return npos;
}

constexpr string_view::size_type string_view::npos;
constexpr string_view::size_type string_view::kMaxSize;

}  // namespace runtime
}  // namespace matxscript
